# ----------------------------------------------------------------------
#   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
#   https://www.lammps.org/ Sandia National Laboratories
#   LAMMPS Development team: developers@lammps.org
#
#   Copyright (2003) Sandia Corporation.  Under the terms of Contract
#   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
#   certain rights in this software.  This software is distributed under
#   the GNU General Public License.
#
#   See the README file in the top-level LAMMPS directory.
# -------------------------------------------------------------------------

"""
Data structures for LAMMPS Python module
Written by Richard Berger <richard.berger@outlook.com>
"""

__all__ = ['NeighList']  # symbols to import with import *

class NeighList:
  """This is a wrapper class that exposes the contents of a neighbor list.

  It can be used like a regular Python list. Each element is a tuple of:

  * the atom local index
  * its number of neighbors
  * and a pointer to an c_int array containing local atom indices of its
    neighbors

  Internally it uses the lower-level LAMMPS C-library interface.

  :param lmp: reference to instance of :py:class:`lammps`
  :type  lmp: lammps
  :param idx: neighbor list index
  :type  idx: int
  """
  def __init__(self, lmp, idx):
    self.lmp = lmp
    self.idx = idx

  def __str__(self):
    # pylint: disable=C0209
    return "Neighbor List ({} atoms)".format(self.size)

  def __repr__(self):
    return self.__str__()

  @property
  def size(self):
    """
    :return: number of elements in neighbor list
    """
    return self.lmp.get_neighlist_size(self.idx)

  def get(self, element):
    """
    Access a specific neighbor list entry. "element" must be a number from 0 to the size-1 of the list

    :return: tuple with atom local index, number of neighbors and ctypes pointer to neighbor's local atom indices
    :rtype:  (int, int, ctypes.POINTER(c_int))
    """
    iatom, numneigh, neighbors = self.lmp.get_neighlist_element_neighbors(self.idx, element)
    return iatom, numneigh, neighbors

  # the methods below implement the iterator interface, so NeighList can be used like a regular Python list

  def __getitem__(self, element):
    return self.get(element)

  def __len__(self):
    return self.size

  def __iter__(self):
    inum = self.size

    for ii in range(inum):
      yield self.get(ii)

  def find(self, iatom):
    """
    Find the neighbor list for a specific (local) atom iatom.
    If there is no list for iatom, (-1, None) is returned.

    :return: tuple with number of neighbors and ctypes pointer to neighbor's local atom indices
    :rtype:  (int, ctypes.POINTER(c_int))
    """

    inum = self.size
    for ii in range(inum):
      idx, numneigh, neighbors = self.get(ii)
      if idx == iatom:
        return numneigh, neighbors

    return -1, None

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